Constraining the properties of asteroid Dimorphos from post-DART impact analysis, semi-analytical models and numerical simulations

NASA's Double Asteroid Redirection Test (DART) impact on asteroid Dimorphos (the smaller component of the 65803 Didymos binary system) occurs on September 26th, 2022. The aim of the mission is to alter the orbital period of Dimorphos around Didymos, which will demonstrate the capabilities of the kinetic impactor as a mitigation strategy for relatively small but, thus, more frequent asteroids. ESA's Hera mission will arrive at Dimorphos about four years after the DART impact and will perform a detailed characterisation of Dimorphos and of the DART impact outcome.

The deflection efficiency of an asteroid can be quantified in terms of a parameter called β, which is the ratio of the momentum of the impactor to the recoil momentum of the target. Past studies of the outcome of small-scale impacts on asteroid surfaces have shown that the impact outcome strongly depends on the surface, subsurface and internal properties. We find that if the target is homogeneous and "strong" (with a strength that is more than a few tens of Pa), then the impact produces a crater and a value of β between 1 and 3.5. If the target is homogeneous and weaker than about 10 Pa, then the impact causes a global deformation of the target and β is expected to be between 4 and 6 . If the target is a rubble-pile (i.e., aggregate held together only by self-gravity and, in some cases, small cohesive forces) with a dense distribution of boulders, then both the impact outcome and β depend on the boulder size-frequency distribution in the body and on the surface properties at the impact location.

In this work we compare the first results from the DART impact (impact location images from the DRACO camera, ejecta plume observed by the Italian Cubesat LICIACube, target characterisation and deflection efficiency estimates) to numerical impact simulations and semi-analytical models results. We aim to constrain the pre-impact mechanical properties of the asteroid.